1. Field of the Invention
The present invention relates in general to product packaging and in particular to a plastic material for forming a good product package having a predictable line of failure when the package is opened to prevent tearing of the bag down the body of the bag. This predictable failure path is provided through a coextruded lamination manufacturing process involving specific resins or blends or resins coextruded in three or more layers that do not inhibit processing speed, efficiency, and economy of materials used to provide this reliable openability.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Laminated films produced for making food packages are based on multiple layers of plastic film each with a specific purpose. An outer web is designed to move across a packaging machine, another web provides heat stability to prevent distortion when the package is sealed, still another provides the ability to obtain a uniform print surface, and yet another provides the ability for the laminated film to be adhered to an adhesive used to bond the laminated film to an adjacent film. When more than two film webs are used to form a laminated film, these core film webs provide additional specific properties such as moisture vapor transfer rate, gas barrier, and appearance. This part of the lamination has nothing to do with the openability of the lamination in package form. The inner web of a lamination can contribute barrier qualities, optics, and sealability, and yet provide openability that varies from "impossible" to "easy open".
Thus, a prior art bag so constructed is illustrated in FIG. 1 wherein the bag 10 is shown filled with product and sealed. It has a longitudinal seal 12 and end seals 14 and 16. The bag is generally made as indicated in FIG. 2 by forming essentially a cylindrical tube 18 with a longitudinal seal 12 and with a horizontal seal at the lower end thereof along seal 16 as shown in FIG. 3. The package can then be filled with product when constructed as shown in FIG. 3 and sealed as illustrated in FIG. 4 to form a bag filled with product having upper and lower sealed ends 14 and 16, respectively, and a longitudinal side seal 12.
The problem with these bags is illustrated in FIG. 5. When the bag is to be opened and forces are applied in the direction of arrows 24 and 26 to the upper seal 14, and bag may start to open at 26 and then tear downwardly into the side of the bag as illustrated at 28. This is not a serious problem for small bags of food products because the contents of the small bag can be eaten entirely. However, with large bags containing large amounts of food products, the tear 28 prevents the bag from being reclosed to protect the contents therein; thus the contents must be transferred to another container that can be sealed to protect the freshness of the product. The reason that such bags tear as shown in FIG. 5 is because of their construction and the interlaminar strength at each interface of the lamination. A history and description of such bag construction is helpful.